1. What is C++?

C++ is a high-level, general-purpose programming language developed by Bjarne Stroustrup as an extension of the C programming language. It supports multiple programming paradigms, including procedural, object-oriented, and generic programming.

2. What are the key features of C++?

Object-Oriented
Rich Standard Library (STL)
Memory Management (Manual and RAII)
High Performance
Multi-paradigm
Low-level manipulation

3. What is the difference between C and C++?

C: Procedural; no classes or objects; no support for function overloading or operator overloading.
C++: Object-oriented; supports classes, objects, inheritance, polymorphism, and templates.

4. What is "Encapsulation" in C++?

The bundling of data and the methods that operate on that data into a single unit (class), while hiding the internal implementation details (using access specifiers like private).

5. What are "Access Specifiers"?

public: Accessible from outside the class.
private: Accessible only within the class.
protected: Accessible within the class and its subclasses.

6. What is a "Constructor"?

A special member function with the same name as the class, automatically called when an object is created. It has no return type.

7. What is a "Destructor"?

A special member function (prefixed with ~) that is automatically called when an object is destroyed or goes out of scope. It's used for cleaning up resources.

8. What is the difference between "Shallow Copy" and "Deep Copy"?

Shallow: Copies member values; pointers point to the same memory.
Deep: Allocates new memory for pointer members and copies the actual data.

9. What is "Inheritance"?

Allows a class (subclass/derived) to inherit properties and behaviors from another class (superclass/base). Types include: Single, Multiple, Hierarchical, Multilevel, and Hybrid.

10. What is "Polymorphism"?

The ability of an object to take on multiple forms:

Compile-time: Function overloading, operator overloading.
Runtime: Virtual functions (Method Overriding).

11. What is a "Virtual Function"?

A function declared in a base class with the virtual keyword, allowing derived classes to provide their own implementation (overriding), which is resolved at runtime (Dynamic Binding).

12. What is a "Pure Virtual Function"?

A virtual function that has no implementation in the base class (e.g., virtual void draw() = 0;).

13. What is an "Abstract Class" in C++?

A class that contains at least one pure virtual function. It cannot be instantiated and serves as a blueprint for derived classes.

14. What is "Operator Overloading"?

Allows you to redefine the behavior of C++ operators (like +, -, *) for custom objects or data types.

15. What is the "this" pointer?

A constant pointer that holds the memory address of the current object. It is implicitly passed to all non-static member functions.

16. What is "Friend Class" and "Friend Function"?

A class or function that is granted access to the private and protected members of another class.

17. What is the difference between `struct` and `class` in C++?

struct: Default access specifier is public.
class: Default access specifier is private.

18. What is "Inline Function"?

A function that the compiler expands in place at each call site to avoid the overhead of a function call. Use the inline keyword.

19. What is "Reference" in C++?

An alias for an already existing variable (e.g., int &ref = x;). It must be initialized at declaration and cannot be reassigned to another variable.

20. What is the difference between a "Pointer" and a "Reference"?

Pointer: Can be null; can be reassigned; requires dereferencing (*).
Reference: Cannot be null; cannot be reassigned; behaves like the variable itself.

21. What is the "STL" (Standard Template Library)?

A collection of template classes and functions for data structures (containers), algorithms, and iterators.

22. What are the common containers in STL?

Sequence: vector, list, deque.
Associative: set, map, multiset, multimap.
Adapters: stack, queue, priority_queue.

23. What is a "Vector" in STL?

A dynamic array that can grow or shrink in size automatically. It provides fast random access.

24. What is "Iterator"?

An object that points to an element within a container and allows you to traverse through the elements.

25. What is "Generics" (Templates) in C++?

Allows you to write code that is independent of a particular data type (e.g., template <typename T>).

26. What is "RAII" (Resource Acquisition Is Initialization)?

A programming idiom where resource management (memory, file handles, locks) is tied to object lifetime (constructor/destructor), preventing leaks.

27. What is "Smart Pointer"?

A class that wraps a raw pointer and automatically manages its lifetime, preventing memory leaks and dangling pointers (e.g., std::unique_ptr, std::shared_ptr).

28. What is the difference between `unique_ptr` and `shared_ptr`?

unique_ptr: Only one owner for the object; cannot be copied.
shared_ptr: Multiple owners via reference counting; object is destroyed when the last owner is gone.

29. What is "Exception Handling" in C++?

Using try, catch, and throw blocks to handle errors and alternative execution paths.

30. What is a "Namespace" in C++?

Used to organize code into logical groups and prevent name collisions (e.g., std::cout).

31. What is "Function Overloading"?

Defining multiple functions with the same name but different parameter lists (type, number, or order).

32. What is "Static Keyword" for class members?

Static Field: Shared across all instances of the class.
Static Method: Can be called without creating an instance; can only access other static members.

33. What is "Const" keyword in C++?

Const Variable: Value cannot change.
Const Pointer: Address or value cannot change.
Const Method: Member function that does not modify the object's state.

34. What is "Mutable" keyword?

Allows a member variable of a const object to be modified from a const member function.

35. What is "L-value" and "R-value" in C++?

L-value: An object that occupies an identifiable location in memory (can appear on the left side of =).
R-value: An object that does not persist beyond the expression (can only appear on the right side of =).

36. What is "Move Semantics" (C++11)?

Allows transferring the contents of an R-value object (like a temporary) to another object, avoiding expensive copies.

37. What is "Lambda Expression" (C++11)?

An anonymous function that can capture variables from its surrounding scope (e.g., [capture](params) -> return { body }).

38. What is "Final" keyword (C++11)?

Final class: Cannot be inherited.
Final method: Cannot be overridden in derived classes.

39. What is the difference between `new`/`delete` and `malloc`/`free`?

new/delete: C++ operators; call constructors/destructors; type-safe.
malloc/free: C library functions; do not call constructors; return void*.

40. What is "Diamond Problem" in multiple inheritance?

A situation where a derived class inherits from two intermediate classes that both inherit from a single base class, causing ambiguity. Solved using virtual inheritance.

41. What is "Virtual Inheritance"?

A technique used to ensure that a base class's members are shared by all classes in a multiple inheritance hierarchy, preventing duplication.

42. What is "Deadlock"?

A situation in multithreading where two or more threads are stuck waiting for each other to release resources, leading to a permanent hang.

43. What is "Mutex"?

A synchronization primitive used to protect shared data from being simultaneously accessed by multiple threads.

44. What is "VTable" and "Vptr"?

VTable (Virtual Table): An internal table created by the compiler for classes with virtual functions, containing function pointers.
Vptr (Virtual Pointer): A hidden pointer in each object of such a class that points to its corresponding VTable.

45. What is "RTTI" (Run-Time Type Information)?

A mechanism that allows the type of an object to be determined at runtime (e.g., dynamic_cast, typeid).

46. What is the difference between `static_cast` and `dynamic_cast`?

static_cast: Compile-time cast; no runtime check.
dynamic_cast: Runtime cast for polymorphic types; returns nullptr on failure.

47. What is "Template Specialization"?

Creating a specific implementation for a template when a particular data type is used (e.g., optimizing for bool).

48. What is "Functor"?

A class that overrides the operator() so that its instances can be called like functions.

49. What is "Tuple" in modern C++?

A fixed-size collection of heterogeneous values, more flexible than std::pair.

50. What is "SFINAE" (Substitution Failure Is Not An Error)?

A C++ template meta-programming principle where the compiler ignores a template during overload resolution if a specific type substitution fails.

C++ Interview Questions

Table of Contents

What is C++?

What are the key features of C++?

What is the difference between C and C++?

What is "Encapsulation" in C++?

What are "Access Specifiers"?

What is a "Constructor"?

What is a "Destructor"?

What is the difference between "Shallow Copy" and "Deep Copy"?

What is "Inheritance"?

What is "Polymorphism"?

What is a "Virtual Function"?

What is a "Pure Virtual Function"?

What is an "Abstract Class" in C++?

What is "Operator Overloading"?

What is the "this" pointer?

What is "Friend Class" and "Friend Function"?

What is the difference between <code>struct</code> and <code>class</code> in C++?

What is "Inline Function"?

What is "Reference" in C++?

What is the difference between a "Pointer" and a "Reference"?

What is the "STL" (Standard Template Library)?

What are the common containers in STL?

What is a "Vector" in STL?

What is "Iterator"?

What is "Generics" (Templates) in C++?

What is "RAII" (Resource Acquisition Is Initialization)?

What is "Smart Pointer"?

What is the difference between <code>unique_ptr</code> and <code>shared_ptr</code>?

What is "Exception Handling" in C++?

What is a "Namespace" in C++?

What is "Function Overloading"?

What is "Static Keyword" for class members?

What is "Const" keyword in C++?

What is "Mutable" keyword?

What is "L-value" and "R-value" in C++?

What is "Move Semantics" (C++11)?

What is "Lambda Expression" (C++11)?

What is "Final" keyword (C++11)?

What is the difference between <code>new</code>/<code>delete</code> and <code>malloc</code>/<code>free</code>?

What is "Diamond Problem" in multiple inheritance?

What is "Virtual Inheritance"?

What is "Deadlock"?

What is "Mutex"?

What is "VTable" and "Vptr"?

What is "RTTI" (Run-Time Type Information)?

What is the difference between <code>static_cast</code> and <code>dynamic_cast</code>?

What is "Template Specialization"?

What is "Functor"?

What is "Tuple" in modern C++?

What is "SFINAE" (Substitution Failure Is Not An Error)?